add <ul> to make valid html

pelican/themes/simple/templates/authors.html

@@ -4,7 +4,10 @@
 
 {% block content %}
     <h1>Authors on {{ SITENAME }}</h1>
+
+    <ul>
     {%- for author, articles in authors|sort %}
         <li><a href="{{ SITEURL }}/{{ author.url }}">{{ author }}</a> ({{ articles|count }})</li>
     {% endfor %}
+    </ul>
 {% endblock %}